1. Field of the Invention
This invention relates to an apparatus for reproducing recording information data from a recording disc.
2. Related Background Art
Well known recording formats for recording information data onto a recording disc such as an optical recording medium include such systems as CAV (Constant Angular Velocity), CLV (Constant Linear Velocity), ZCAV (Zoned CAV), and ZCLV (Zoned CLV). In the ZCLV system, CAV zones and transition zones are concentrically alternately arranged in one recording disc. In the CAV zone, the recording and reproduction are performed by setting a rotational angular velocity of the disc to be constant, while in the transition zone, the recording and reproduction are performed with the rotational angular velocity of the disc changing.
Japanese patent Kokai No. 7-114733 (designated as “JPA '733-hereinafter) discloses a recording disc using both the sampled servo system and the ZCLV system.
FIG. 1 is a plan view showing a recording surface of the recording disc disclosed in JPA '733.
As shown in FIG. 1, the recording disc comprises an annular recording area 20 including a spiral (or a plurality of concentric) recording track(s) 10 with information signals including a sync signal. In the recording area 20, a zone 21 as a CAV zone, and a boundary area 33 as a transition zone are concentrically alternately formed. A width of track pitch d1 of the boundary area 33 is larger than a track pitch d2 in the zone 21. Servo areas 31a shown by circles in FIG. 1 are intermittently formed on the recording track 10 so that a sampled servo tracking system applies a tracking servo. Further, as shown in FIG. 1, the servo areas 31a are formed in each zone 21 so as to be aligned in the same disc radial direction.
FIG. 2 is a diagram showing a recording format used in the servo area 31a. 
The servo area 31a comprises: a pair of wobble pits 50 for a tracking servo; a mirror surface portion 51 for synchronization and a focusing servo; and clock pits 52 for clock reproduction. Each pair of wobble pits is arranged so as to be deviated in the disc radial direction by an equal distance around the track center. The wobble pit pairs are arranged in a manner such that the wobble pit pair of the odd-number track and the wobble pit pair of the even-number track are deviated in the track direction, respectively. In the tracking servo of the sampled servo system, the position in the disc radial direction of the pickup is controlled so that levels of reproduction signals of the pair of wobble pits are equal.
In the recording disc, a recording density is increased by narrowing the track pitch d2. In the disc, since the wobble pit pair of the odd-number track and the wobble pit pair of the even-number track are arranged so as to be deviated in the track direction as mentioned above, an unnecessary interference by the wobble pits of the adjacent tracks does not occur, even if the track pitch d2 is narrowed. Since the rotational angular velocity of the disc changes in the boundary area 33, however, it is impossible to align the servo areas 31a in the same disc radial direction. If the track pitch d1 is narrowed in a manner similar to d2, therefore, the reproduction signal is subjected to the unnecessary interference by the adjacent tracks. Therefore, the stable tracking servo is not performed. Thus, in the recording disc, the track pitch d1 in the boundary area 33 is set to be larger than d2 so as not to cause the unnecessary interference by the adjacent tracks.
The following problems arise when the recording information is reproduced from the recording disc. When the reproducing apparatus performs the searching operation after completion of the jumping operation of the pickup, the mirror surface portion 51 is first detected and the synchronization and focusing servo are established. Subsequently, the wobble pits are detected, the tracking servo is performed, the clock pits are detected, and the clock reproduction is performed. That is, it is necessary to first detect the mirror surface portion 51 to re-activate the reproducing apparatus after completion of the jumping operation of the pickup. If a jump destination of the pickup is the boundary area 33, it is not guaranteed that the mirror surface portion 51 can be positively detected, since the servo areas 31a are not aligned. Since it takes more time to re-activate the reproducing apparatus than necessary or the re-activation fails, a case may occur where the searching operation becomes unstable. Even when the boundary area 33 is jumped and searched, in the case where the pickup jumps over a portion other than the servo areas 31a, a tracking error cannot be detected, so that the count number of the track jump is incorrect, and search time increases.